1. Field of the Invention
The present invention relates to a communication method and corresponding device in a wireless mobile communication system, particularly for a cellular system.
2. Discussion of the Related Art
In wireless communications, diversity gain is the increase in a signal-to-interference ratio achieved due to some diversity scheme. In other words, diversity gain represents how much the transmission power can be reduced when a diversity scheme is introduced, usually without a performance loss.
In telecommunications, a diversity scheme may relate to a method for improving the reliability of a message signal by using two or more communication channels with different characteristics. Diversity plays an important role in combating fading and co-channel interference and avoiding error bursts. The benefits achieved through diversity scheme are based on the fact that individual channels often experience different levels of fading and/or interference. Thus, multiple versions of the same signal may be transmitted and/or received and combined in the receiver to overcome fading and/or interference associated with a single signal.
Frequency diversity is a type of diversity scheme in which a signal is transferred using several frequency channels or is spread over a wide spectrum that is affected by frequency-selective fading.
In a system adopting orthogonal frequency division multiple access (OFDMA), a resource unit typically indicates a set of resource elements comprising Psc subcarriers by Nsym consecutive OFDMA symbols. Resource units are usually classified into a physical resource unit (PRU) type and a logical resource unit (LRU) type. A PRU is the basic physical unit for resource allocation that comprises Psc consecutive subcarriers by Nsym consecutive OFDMA symbols. A LRU is the basic logical unit for distributed and localized resource allocations. A PRU or LRU can be indexed by the frequency value of the subcarrier of the PRU or LRU.
To obtain diversity gain, resource units (RUs) in the frequency/time domain can be spread along a frequency axis by a predetermined permutation rule designed for obtaining frequency diversity gain. Permutation may be considered to be a mapping of elements of a set to other elements of the same set, i.e., exchanging (or “permuting”) elements of a set. Alternatively, permutation can be regarded as an assignment operation, with the indexes of a set of the PRUs assigned to the indexes of a set of the LRUs. In some cases, each index is assigned only once.
In some schemes, a part of one or more LRUs can be used to obtain the above described diversity gain, and another part of the one or more LRUs can be used to obtain a band scheduling gain or a frequency scheduling gain. The band scheduling gain is attainable by allocating consecutive PRUs to a user equipment (UE), knowing that the frequency band corresponding to the allocated consecutive PRUs is the optimum frequency channel for the UE. Some control information, i.e., an overhead signal, may be communicated between a transmitter and a receiver to deliver the knowledge of the optimum frequency channel.
Permutation of resource units (RUs) can be performed in units of N RUs (N>=1), i.e., with a granularity of N. In some cases, if the value of N decreases, the frequency diversity gain by permutation increases, and vice versa. However, in these cases, if the value of N decreases, the amount of the control information increases, which increases system overhead. That is, the benefit in terms of frequency diversity gain may turn into a disadvantage in terms of a signaling overhead resulting from band scheduling gain. Therefore, as discovered by the present inventors, a need has arisen to balance frequency diversity gain and overhead by communicating in accordance with an optimum number N for a given communication system requirement.